DE 103 04 364 A1 describes a throttle arrangement and an exhaust system of the type defined above. The known throttle arrangement includes a throttle valve for throttling an exhaust gas stream flowing through a pipe and a restoring spring applying prestress to the throttle valve pulling it into the closed position. The throttle valve is pivotable about a pivot axis in the pipe between the closed position, in which it at least partially closes a predetermined cross-sectional area of the pipe, and an open position, in which it releases the cross-sectional area due to the pressure of the exhaust gas against the spring force of the restoring spring. With the known throttle arrangement, the restoring spring is designed as a leg-spring whose helical spring section is arranged coaxially with a shaft that in turn extends coaxially with the pivot axis of the throttle valve. The shaft is arranged in a lateral recess in the pipe that is open toward the exhaust gas flow. The leg spring is supported with a free leg on a lever fixedly connected to the throttle valve and is supported with the other free leg on a wall of the aforementioned recess. The restoring spring is thus supported on the lever on the valve end and on the pipe on the pipe end and/or on a bearing to accommodate the shaft.
It has been found that in operation of the throttle arrangement in adjustment of the throttle valve, friction occurs between the restoring spring and neighboring components on the one hand and between the throttle valve and the pipe on the other hand. First, the helical spring section of the restoring spring may grind against the shaft in particular. Owing to the frequent adjusting movements of the throttle valve that occur during operation of the internal combustion engine, there may be abrasion and therefore weakening of the material of the restoring spring. Weakening of the material in an area of the restoring spring that is important for the spring elasticity can alter its spring characteristic, which has a negative effect on the function of the throttle arrangement. For example, one or more windings of the helical spring section may be weakened due to friction on the shaft, so the leg spring then has a softer spring characteristic. In the extreme case, continued friction can destroy the restoring spring. For example, the leg spring may break in its helical spring section. The restoring spring is then virtually ineffective and the throttle arrangement then fails. In addition, the throttle valve may also grind on the pipe, making it difficult to operate, and with progressive soiling, it may even jam and ultimately seize up. This can also lessen the efficacy of the throttle arrangement, leading to total failure.